(a) Technical Field
The present disclosure relates to a piston ring for engine wherein low friction Si-DLC is coated on the peripheral surface of the piston ring to reduce friction loss in an engine cylinder and to improve fuel efficiency, and a method for manufacturing thereof.
(b) Background Art
A piston ring is a pair of rings that fits into a groove on the outer diameter of a piston to maintain air tightness between a piston of a vehicle engine and inner cylinder wall, and to prevent entering lubricating oil to a combustion chamber by scraping out the lubricating oil of the cylinder wall.
FIG. 1 is a drawing representing coating condition of the existing piston ring for engine. In this conventional piston ring design, the piston ring has difficulty maintaining durability due to its low friction efficiency. Generally, Cr (Chrome) plating 30 or nitriding (gas nitriding) is being used on the peripheral surface of the piston ring 10, and recently, due to high fuel cost and CO2 regulation, various surface treatment techniques including CrN (Chrome Nitride) are also becoming more popular for reducing friction loss and improving durability.
Furthermore, methods like DLC (Diamond Like Carbon), which is an intermediate phase of diamond and graphite, and has low friction coefficient of graphite, high rigidity of diamonds and excellent chemical resistance, can further reduce friction loss of the engine when it is applied to the peripheral surface of the piston ring and can improve fuel efficiency of a vehicle in the end. However, the friction and durability of DLC becomes worse when it is exposed to higher temperatures for a long period of time, and coating is exfoliated due to high residual stress in the coating as the coating becomes thicker.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.